1. Field of the Invention
The inventions proposed are related to X-ray means for detecting of the elastic strains present in single-crystal wafers and are intended, in particular, for use in monitoring of the manufacturing process of printed-circuit substrates in microelectronics.
2. Description of Related Art
A method is known for detection of elastic strains present in a single crystal, is based on its interaction with monochromatic infrared radiation (see Y. Kawano et al., Infra Red System GaAs/AlGaAs., J. Appl. Phys. 2001, 89, p. 4037 [1]). At the sites of disturbances of periodicity and orientation of crystal lattice the interference maxima of infrared radiation are observed, and registered by semiconductor sensors.
In single-crystal materials with metallic interatomic bonds (germanium, silicon, arsenic, and others), transmission over them of thermal vibrations results in broadening of said maxima and rising of background level up to their merging. This makes the usage of said method in manufacturing wide assortment of single-crystal wafers impossible.
Also known is X-ray method for detection of elastic strains located in single-crystal wafers (see O. Brümmer. Zeitschrift für Naturforschungen, 15A, S.875, 1960 [2]).
This method is based on detection of crystallographic planes departures from relative orientation.
Surface of single-crystal wafer is illuminated with widely diverging X-ray beam. Diffracted radiation is registered with a flat X-ray film. The recorded diffraction of the interference pattern is compared with a reference pattern obtained for reference standard single-crystal wafer, and a conclusion about presence or absence of elastic strains in single-crystal wafer inspected is reached by the degree of their divergence. Angular divergence of illuminating beam is adjusted so as to ensure fulfillment of diffraction conditions for two or three sets of crystallographic planes. For the most of widely used materials of single-crystal wafers said angular divergence of illuminating beam can reached of 30–40°.
Using of a beam having such a large divergence implies large illuminated surface area of single-crystal wafer participating in diffraction and, as a consequence, results in generation of averaged interference pattern, induced by diffraction in different geometric points of a surface. Therefore, unambiguous interpretation of interference pattern of diffraction registered on the film is made difficult. Because of this, high probability of erroneous results of the control. Besides, photographic method of registration used requires large exposure times (several hours) as well as some satisfactions simultaneously the requirements to resolution and contrast. This constitutes the principal obstacle to establishing complete control in flow-line production, thus inducing forcedly random testing of a small number of wafers.
Method and device known from [2] are the most close ones to those proposed.